Field of the Invention
The present invention relates to a program creating device for a wire electric discharge machine, furnished with a loading unit capable of arbitrarily tilting a workpiece using two or more pivots.
Description of the Related Art
FIG. 12 illustrates taper machining in which an upper guide portion is moved parallel to a table surface in a wire electric discharge machine so that a wire electrode 4 supported by a wire guide portion is stretched obliquely relative to a vertical direction 5. In the conventional taper machining, as shown in FIG. 12, a workpiece 3 placed on a table 2 is discharge-machined with the wire electrode 4 tilted relative to the vertical direction 5.
The taper machining in which the wire electrode 4 is stretched obliquely relative to the vertical direction 5 has more technical problems than vertical machining in which the wire electrode 4 is stretched vertically. The major problems are as follows:
(1) The machining speed cannot be increased due to difficulties in discharging sludge.
(2) The wire guide portion applies frictional force, thereby adversely affecting the surface roughness.
(3) Since supporting points of the wire electrode bent by the wire guide portion vary depending on the shape precision of the guide portion and the state of the guide portion during the machining, high-precision is difficult.
(4) It is difficult to set machining conditions.
These problems are caused because the wire electrode is obliquely stretched and they become more serious as the taper angle increases.
Thereupon, Japanese Patent Application Laid-Open No. 2012-254505 discloses a wire electric discharge machine that comprises a table having a plane and a coordinate system based on two orthogonal axes and configured to carry a workpiece thereon. This discharge machine performs electric discharge machining while relatively moving a wire electrode and the workpiece according to a machining program. The wire electric discharge machine comprises a loading unit, tilt angle setting unit, coordinate system conversion unit, and machining command value correction unit. The workpiece is placed on the loading unit so that it is tilted relative to the plane of the table. The tilt angle setting unit sets a tilt angle between the plane and the tilted workpiece on the loading unit. The coordinate system conversion unit tilts the coordinate system at the set tilt angle. The machining command value correction unit corrects a machining command value commanded by the machining program.
The wire electric discharge machine disclosed in Japanese Patent Application Laid-Open No. 2012-254505 is configured to machine the workpiece tilted at a fixed angle so that the tilt of the wire electrode can be reduced to solve the problems of the tilt machining. In reality, however, the wire electrode is inevitably tilted, though slightly. Thus, the aforementioned problems attributable to the oblique stretching of the wire electrode cannot be fully avoided.